Known mobile wireless communication systems include those such as WCDMA (Wideband Code-Division Multiple Access), LTE (Long Term Evolution), LTE-A (LTE-Advanced) and WiMAX (Worldwide Interoperability for Microwave Access), in accordance with 3GPP (Third Generation Partnership Project). In these mobile wireless communication systems, an area that is covered by a base station (base station apparatus, transmitting station, transmitter apparatus, eNodeB) or a transmitting station that is in accordance with a base station has a cellular configuration in which a plurality of cells are disposed, thereby enabling an expansion of the communication area.
By using different frequencies between adjacent cells or between adjacent sectors, even for terminal devices (receiver apparatuses, receiving stations, mobile stations, mobile terminals, UE (user equipment)) in a cell edge region or a sector edge region, it is possible to perform communication without interference from the transmitted signals from a plurality of base stations. In this case, however, there is the problem of a poor rate of frequency spectrum utilization. By using the same frequency between adjacent cells or sectors, it is possible to improve the rate of frequency spectrum utilization. In this case, however, interference countermeasures are necessary to handle interference to terminal devices positioned in a cell edge region.
A method of suppressing interference with respect to terminal devices in a cell edge region by performing cooperative communication between cells, in which there is mutual cooperation between adjacent cells is under study as such an interference countermeasure. As such a method, Non-Patent Document 1 discloses a CoMP (Cooperative Multipoint) transfer system (cooperative communication system) and the like. As the CoMP system, disclosure is made of joint processing, in which cooperative transmission is done of the same or different data between cells, joint transmission, coordinated scheduling, in which scheduling and controlling is done by coordination between cells, and beamforming.
By performing adaptive control of the modulation method, the coding scheme (MCS: Modulation and Coding Scheme), the spatial multiplexing (layers and ranks) and precoding weight (precoding matrix) in accordance with the transfer status between a base station and a terminal device, it is possible to achieve data transfer with improved efficiency. Non-Patent Document 2 discloses a method that applies these types of control.
FIG. 17 is a drawing that shows a base station 1701 and a terminal device 1702 that perform non-cooperative communication (non-CoMP) with, for example, MIMO (multiple-input multiple-output) transmission from a single cell in LTE-A. A proposal is made of the terminal device 1702 in LTE-A using a reference signal (RS) transmitted from the base station 1701, a pilot signal, a known signal, and a propagation channel status measurement reference signal, the CSI-RS (Channel State Information RS) to transmit feedback information to the base station 1701. The reference signal is transmitted to the terminal device 1702 from the base station 1701.
The terminal device 1702 transmits feedback information generated based on the reference signal to base station 1701. In the case of the downlink used for data transfer from the base station 1701 to the terminal device 1702, in order to perform the above-noted adaptive control, the downlink propagation channel status or the like is estimated at the terminal device 1702 based on the reference signal transmitted from the base station 1701. Then, estimated propagation channel status or the like is transmitted (fed back) to the base station 1701 via the uplink that performs data transfer from the terminal device 1702 to the base station 1701. Non-Patent Document 3 proposes the placement of a reference signal in only some of the subframes, rather than locating the reference signal in all subframes on the time axis when locating the reference signal.
FIG. 18 is a drawing showing an example of a reference signal transmitted to the base station 1701. In FIG. 18, the horizontal axis indicates time and the vertical axis indicates frequency. The various square regions within a resource block (RB) 1801 that is defined by a prescribed time and frequency indicate resource elements (this indicates the region in which the modulating symbol is mapped REs). The reference numerals 1801-1 to 1801-4 indicate resource elements onto which the LTE-A reference signal is mapped. The reference numeral 1801-5 indicates the resource element onto which the LTE reference signal is mapped.
The reference numeral 1801-6 indicates a resource element onto which a signal other than the reference signal (that is, a data signal or control signal or the like) is mapped. As the position of the reference signal, it is possible to use a reference signal scattered among the resource elements in the frequency direction and the time direction. The UE in the LTE-A system can use information that indicates the channel characteristics (CSI: Channel State Information), the recommended transmission format information with respect to the base station (CQI: Channel Quality Indicator), and the RI (Rank Indicator) and PMI (Precoding Matrix Index) as the information (feedback information) to the base station, which is generated based on this LTE-A reference signal.
FIG. 19 is a drawing showing a base station 1901, a base station 1902, and a terminal device 1903 that perform CoMP communication in the LTE-A system. A proposal has been made for the terminal device 1903 using the reference signals transmitted from each of the base stations 1901 and 1902 to generate feedback information, and transmitting the generated feedback information to the base station 1901 in the LTE-A system. In Non-Patent Document 4, there is a proposal for puncturing data from the base station 1902 at the terminal device 1903 when the reference signal is transmitted from the base station 1901, for the purpose of measuring the reference signal with high accuracy when performing CoMP communication in the LTE-A system (that is, data is not mapped onto the resource element, or data transmission is stopped).